Water developable diazo based lithographic printing plate comprising an intermediate layer having a polysaccharide

Abstract

The present invention provides an imaging element comprising on a support in the order given, a hydrophilic layer containing a hydrophilic (co)polymer or (co)polymer mixture and being hardened with a hydrolyzed tetraalkyl orthosilicate crosslinking agent and a light sensitive layer containing a diazo resin or a diazonium salt characterized in that an intermediate hydrophilic layer containing an organic compound having one or more cationic groups is provided between said hydrophilic layer and said light-sensitive layer. There is further provided a method for making such an imaging element and a method for making a lithographic printing plate therewith.

We claim: 
     
       1. An imaging element comprising on a support in the order given, a hydrophilic layer containing a hydrophilic (co)polymer or (co)polymer mixture and being hardened with a hydrolyzed tetraalkyl orthosilicate crosslinking agent and a light-sensitive layer containing a diazo resin or a diazonium salt, an intermediate hydrophilic layer containing an organic compound having one or more cationic groups between said hydrophilic layer and said light-sensitive layer, said organic compound being a hydrophilic polysaccharide having one or more ammonium groups or a hydrophilic polysaccharide and a low molecular weight organic compound having one or more ammonium groups. 
     
     
       2. An imaging element according to claim 1 wherein said polysacharide is dextran or pullulan. 
     
     
       3. An imaging element according to claim 1 wherein said organic compound is comprised in said imaging element in an amount between 5 and 500 mg/m 2 .